Kidney function II, Clearance and use in renal physiology Flashcards
Definition of clearance
Measure of volume of plasma from which a substance is completely removed per unit time
Definition of osmolality
Conc of a solution expressed as a total no of solute particles/kg
Definition of osmolarity
Conc of a solution expressed as the total no of solute particles/l
Definition of counter current multiplier
A system where energy is used to transport materials across a membrane separating 2 countercurrent multiplier tubes connected at 1 end to form a hairpin shape
Renal clearance equation
What is clearance
Volume of plasma cleared of substance in time
Renal clearance = UV/P
U = [in urine] V = volume of urine/min P = [in plasma]
How is GFR measured
- experimentally
- clinically
Why is this substance used?
What are the limitations of clinical measuring
Clearance of inulin/creatine (slightly secreted => slight overestimate
- Freely filtered
- Not reabsorbed or secreted or metabolised
- Easily measured
How is PAH processed in the kidney
How does this relates to the renal plasma flow
How would you use this to calculate the renal blood flow
Filtered and completely secreted
Rate of excretion = renal plasma flow (600ml/min)
Slight underestimate, only considers plasma flow through kidney
Renal blood flow = plasma flow/1-haematocrit = 1100ml/min
Describe the osmolarity of
- plasma
- urine
Why is it important to control osmolarity in the blood
Plasma
- 300 mosmol/kg
- must be controlled, affects BV, BP via Na
Urine
-50-1400 mosmol/kg
Describe how Na is reabsorbed in the
- PT
- Thick ascending LOH
- Thin ascending LOH
- DT
- CD
PT
-Cotransported with other solutes, driven by NaKATPase
-NaH exchange => into cell
Cotransported with HCO3 => into medulla
Thick asc LOH
-NaClK triporter => into cell, driven by NaKATPase
Thin asc LOH
-Passive
DT
-NaCl channel => cell, driven by NaKATPase
CD
-Principle cell ENaC => into cell, driven by NaKATPase
How is water reabsorbed in the
- PT
- Counter current multiplier in the LOH
- CD
PT
-Follow Na via AQP1 channels/paracrinly
Counter current multiplier
- Asc limb reabsorbs NaKCl => vasa recta => increased osmolarity
- Desc limb reabsorbs water via AQP1 => decreased osmolarity
- Osmolarity of medullar increases as you descend
CD
-Via AQP1-4
How is urea reabsorbed and secreted in the
- PT
- LOH
- CD
PT
-Passive reabsorption
LOH
- UTA2 secretion => desc LOH
- Passive secretion => asc LOH
CD
- UTA1, 3 reabsorption => increased osmolarity in medulla
- Increases water reabsorption
Where are these urea transporters found What are their functions -UTA1 -UTA2 -UTA3 -UTB
UTA1
- CD
- CD => epithelium
- affected by ADH
UTA2
- Asc LOH
- Epithelium => asc LOH
UTA3
- CD
- Epithelium => Medulla
- affected by ADH
UTB
-VR => medulla
Describe the mechanism of ADH
What structures does it act on
ADH binds to V2 receptor (GPCR)
ATP =(AC)=> cAMP
cAMP acts on PKA
PKA stimulates fusion of AQP2 vesicles
DCT
CD
How do we produce concentrated urine
Medulla osmolarity increases due to urea reabsorption
Leads to water reabsorption=> urine osmolarity increases
What is the function of the distal convoluted tubule
Adjust the balance of ions in the blood
Impermeable to water, urea
ADH can still act here
